Area Forecast Discussion
Issued by NWS Mt. Holly, NJ

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000 FXUS61 KPHI 270808 AFDPHI AREA FORECAST DISCUSSION NATIONAL WEATHER SERVICE MOUNT HOLLY NJ 408 AM EDT MON JUL 27 2015 .SYNOPSIS...
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A WEAKENING COLD FRONT OVER PENNSYLVANIA IS EXPECTED TO DISSIPATE TODAY OVER OUR AREA. A HIGH PRESSURE SYSTEM WILL THEN BUILD BACK OVER THE MIDDLE ATLANTIC STATES FOR THE MIDDLE OF THE WEEK. ANOTHER COLD FRONT SHOULD MOVE THROUGH THE REGION AROUND THURSDAY NIGHT. A WEAK HIGH PRESSURE SYSTEM SHOULD THEN BUILD INTO THE NORTHEAST LATER FRIDAY INTO THE WEEKEND.
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&& .NEAR TERM /UNTIL 6 PM THIS EVENING/... THE SYNOPTIC SETUP IS COMPRISED OF NORTHWEST FLOW ALOFT WITH AN EMBEDDED SHORT WAVE TROUGH. THIS FEATURE WILL CROSS OUR AREA DURING THE COURSE OF TODAY. THE CONTINUATION OF PVA WITH LINGERING INSTABILITY AND VEERING FLOW WITH HEIGHT IN THE LOWER TO MID LEVELS IS MAINTAINING CONVECTION EARLY THIS MORNING. THE FLOW/SHEAR IS ON THE LIGHTER SIDE, HOWEVER ORGANIZATION IS BEING MAINTAINED PROBABLY DUE TO COLD POOLS AND NEW UPDRAFT CORES ALONG THE LEADING EDGE. THE MODEL GUIDANCE IN GENERAL SUGGESTS THAT A GRADUAL WEAKENING TREND OCCURS WITH AN EASTERN EXTENT FOR AWHILE THIS MORNING BEFORE ADDITIONAL ACTIVITY DEVELOPS WITH RENEWED HEATING WITHIN INCREASING INSTABILITY. THEREFORE WE BUMPED UP POPS QUITE A BIT FOR A TIME THIS MORNING THEN TRENDED BACK TOWARD THE CHC RANGE FOR MOST OF THE AREA. THE PW VALUES ARE AROUND 1.5 INCHES, AND THIS COMBINED WITH CLUSTERING OF THE CONVECTIVE UPDRAFTS /EVEN SOME BACK BUILDING/ EARLY THIS MORNING IS LEADING TO VERY HEAVY RAINFALL IN SOME AREAS. THIS WILL PRODUCE SOME LOCALIZED FLOODING. IT DOES NOT APPEAR A LOT OF LIFT IS NEEDED WITHIN THE AIRMASS TO PROMOTE NEW DEVELOPMENT AS A WEAKENING COLD FRONT GENERALLY DISSIPATES INTO OUR AREA. A WEAK SURFACE TROUGH MAY PERSIST THOUGH AND HELP FOCUS SOME NEW DEVELOPMENT THROUGH THE DAY. AS FOR THE HIGH TEMPERATURES, WE MOSTLY WENT WITH A NAM/GFS MOS BLEND WITH THE ANTICIPATION OF ENOUGH CLOUDS AND CONVECTION AROUND. && .SHORT TERM /6 PM THIS EVENING THROUGH 6 AM TUESDAY/... THE SHORT WAVE TROUGH IS FORECAST TO SHIFT TO OUR EAST THIS EVENING, AND THEN SOME SUBTLE HEIGHT RISES OCCUR AS SLIGHT RIDGING STARTS TO ARRIVE FROM THE WEST. AS A RESULT, THE PVA WITHIN THE NORTHWESTERLY FLOW ALOFT IS FORECAST TO WANE AND THIS SHOULD ALLOW ANY CONVECTION TO DISSIPATE BY LATE EVENING FOR MUCH OF THE AREA. THEREFORE, WE TRENDED THE POPS DOWNWARD THROUGH THE EVENING WITH THE LAST MENTIONABLE CONVECTION IN PORTIONS OF THE DELMARVA OVERNIGHT. OTHERWISE, SOME PARTIAL CLEARING SHOULD TAKE PLACE FROM THE NORTHWEST ALTHOUGH SOME HIGH LEVEL CLOUDS MAY CONTINUE TO MOVE ACROSS. THE PRESENCE OF LIGHT WINDS AND AREAS OF LESSENING CLOUD COVER MAY RESULT IN LOCAL FOG DEVELOPMENT OVERNIGHT, ESPECIALLY IN AREAS WHERE HEAVY RAIN HAS FALLEN WHICH WILL ASSIST IN LOW-LEVEL MOISTURE POOLING. THIS MAY BE LOCALIZED ENOUGH THEREFORE IT WAS NOT INCLUDED ATTM. AS FOR THE LOW TEMPERATURES, WE SIDED WITH A GFS/NAM MOS BLEND WITH SOME MINOR LOCAL TWEAKS. && .LONG TERM /TUESDAY THROUGH SUNDAY/...
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THE MODEL TENDENCY OF THE LAST COUPLE OF DAYS HAS CONTINUED TONIGHT WITH THE GFS HAVING A BETTER 500MB INITIALIZATION AND THE WRF- NMMB A BETTER 850MB AND 925MB INITIALIZATION AS THE GFS WAS TOO WARM WITH ITS ERRORS. THIS INCLUDED THE NORTHERN PLAINS. MOVING FORWARD TO THE ACTUAL MODEL THERMAL RUN, THE GFS IS MORE IN LINE WITH THE SREF AND THE ECMWF THAN THE OP WRF-NMMB WHICH IS ON THE HOT SIDE. NOT SURPRISING THAT THE DP/DT ON THE GFS IS SLOWER WITH THE CFP PASSAGE THURSDAY. BECAUSE OF THE ONGOING HEAVY RAIN IN OUR CWA, THE LONG TERM WAS HEAVILY WEIGHTED TOWARD A CONTINUITY AND WPC BLEND. HEAT RELATED HEADLINES REMAIN A POSSIBILITY FOR WEDNESDAY AND THURSDAY ESPECIALLY IN URBAN AREAS. THERE IS STILL SOME UNCERTAINTY AS TO WHETHER ONE OR TWO DAYS WILL MEET THE CRITERIA, SO WE CONTINUED MENTION IN THE HWO, BUT DID NOT ISSUE A WATCH. ON TUESDAY, A MID LEVEL CAP IS PREDICTED TO DEVELOP ACROSS MOST OF OUR CWA. THE LATEST AND WEAKEST ARRIVAL IS IN THE SOUTHERN PART OF OUR CWA WHERE WE KEPT A LOW CHANCE OF AFTERNOON THUNDERSTORMS. THE GFS HAS HAD DECENT RUN TO RUN CONTINUITY IMPLYING THAT BAY BREEZES MAY BE THE THUNDERSTORM TRIGGER. IRONICALLY, BECAUSE OF A DEVELOPING OFFSHORE LOW, COOLER AIR WRAPS BACK TOWARD THE DELMARVA AND SOUTHERN NEW JERSEY COAST. THIS IS ALL RELATIVE BECAUSE THE AIR MASS IS STILL SUMMER TIME WARM. BUT, THE TOPSY-TURVEY THERMAL PICTURE CONTINUES AS SUSSEX COUNTY NEW JERSEY MAY HAVE HIGHER TEMPS THAN SUSSEX COUNTY DELAWARE. 10C ADDED TO PREDICTED 925 TEMPS HAVE WORKED THE BEST THE LAST COUPLE OF DAYS FOR MAX TEMPS AND WAS USED AGAIN. STAT GUIDANCE WAS PRETTY CLOSE ALSO. THE WINDS ARE NOT EXPECTED TO BE THAT STRONG, BUT THERE IS DRY AIR ALOFT AND DEW POINTS SHOULD DROP A BIT, ESPECIALLY THE NORTHWEST TWO THIRDS OF OUR CWA. FROM TUESDAY NIGHT THROUGH WEDNESDAY NIGHT, THE SURFACE HIGH PRESSURE SYSTEM WILL BE MORE IN CONTROL AND NO PRECIPITATION IS FORECAST. WEDNESDAY WILL BE HOTTER WITH NEARLY ALL OF OUR CWA REACHING INTO THE LOWER AND MID 90S. THE STICKING POINT FOR REACHING HEAT HEADLINE CRITERIA MAY BE THE DEW POINTS. DISGUSTING MID 70S OR HIGHER DEW POINTS ARE STILL GEOGRAPHICALLY PRETTY FAR REMOVED FROM OUR AREA AND WITH THE HIGH PRESSURE SYSTEM IN PLACE OVER US, NOT MUCH OF AN ADVECTION FACTOR INVOLVED YET. THERMALLY WE ARE STILL JUXTAPOSITIONED, PRETTY UNIFORM (EXCEPT FOR ELEVATION AND SHORE POINTS) IN MAX TEMPS. A VERY WARM WEDNESDAY NIGHT EXPECTED. GFS HAS BACKED AWAY FROM A FASTER COLD FRONTAL PASSAGE TIMING AND NEVER CONFIDENT ABOUT A COLD FRONT SAVING THE DAY FROM THE HEAT IN SUMMER. THE ECMWF FROM A FEW DAYS AGO HAS WENT THE GFS`S WAY THERMALLY ALTHOUGH ITS STAT GUIDANCE REMAINS STRANGELY LOW WITH MAINLY LOWER 90S FOR HIGHS. NCEP GUIDANCE CONTINUES TO POINT TO THIS DAY AS THE MOST LIKELY TO REACH HEAT HEADLINES. WITH AN APPROACHING COLD FRONT TO POOL DEW POINTS AND A STRONGER SOUTHWEST FLOW TO ADVECT THOSE NASTY DEW POINTS IN, THIS APPEARS LOGICAL. MODELS NOT TERRIBLY ENTHUSED ABOUT THUNDER, SHOWING THE ENERGY SPLIT. WE KEPT THE CONTINUITY GOING WITH LEAVING POPS AS CHANCE. NOT MANY CHANGES TO THE REST OF THE LONG TERM. THE COLD FRONTAL PASSAGE SHOULD BRING ONLY SLIGHTLY COOLER, MORE IMPORTANTLY, DRIER AIR INTO OUR CWA ON FRIDAY AND SATURDAY. SOME MAX TEMPS SHOULD STILL REACH 90, BUT THE HEAT INDEX AND MAX TEMPS WILL BE CLOSER TO ONE AND THE SAME. AN APPROACHING COLD FRONT FOR SUNDAY BRINGS PRECIPITATION CHANCES BACK THROUGHOUT OUR CWA.
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&& .AVIATION /08Z MONDAY THROUGH FRIDAY/...
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THE FOLLOWING DISCUSSION IS FOR KPHL, KPNE, KTTN, KABE, KRDG, KILG, KMIV, KACY AND SURROUNDING AREAS. TODAY...SHOWERS AND SOME THUNDERSTORMS EARLY THIS MORNING SETTLING EASTWARD ACROSS MUCH OF THE AREA. THIS WILL RESULT IN A TIME OF MVFR/IFR CONDITIONS ESPECIALLY VISIBILITIES. OUTSIDE OF ANY SHOWERS AND THUNDERSTORMS, VFR IS ANTICIPATED /LOCAL LIGHT FOG POSSIBLE EARLY THIS MORNING/. SOME SHOWERS AND THUNDERSTORMS ARE EXPECTED THROUGH THE DAY, HOWEVER CARRIED A TEMPO FOR SHOWERS AS THUNDERSTORM PLACEMENT AFTER THE EARLY MORNING ACTIVITY IS A BIT UNCERTAIN. SOUTH- SOUTHWEST WINDS GENERALLY 5-10 KNOTS. TONIGHT...SOME SHOWERS AND THUNDERSTORMS WITH BRIEFLY REDUCED VISIBILITIES AND/OR CEILINGS IN THE EVENING ARE EXPECTED TO DIMINISH. THERE IS THE CHANCE FOR LOCAL FOG TO DEVELOP LATE. SOUTHERLY WINDS 5 KNOTS OR LESS. OUTLOOK... TUESDAY...MAINLY VFR. ISOLATED AFTN THUNDERSTORMS POSSIBLE SOUTH. TUESDAY NIGHT THROUGH WEDNESDAY...VFR CONDITIONS EXPECTED. WEDNESDAY NIGHT...SOME MVFR CONDITIONS DUE TO VSBY RESTRICTIONS POSSIBLE AT MORE RURAL AIRPORTS AND TERMINALS. THURSDAY AND THURSDAY NIGHT...VFR. BUT POCKETS OF MVFR TO IFR CONDITIONS AS SCATTERED SHOWERS AND THUNDERSTORMS MOVE THROUGH. FRIDAY...SOME PATCHY RESTRICTIVE FOG EARLY, OTHERWISE VFR.
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&& .MARINE...
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THE CONDITIONS ARE ANTICIPATED TO REMAIN BELOW SMALL CRAFT ADVISORY CRITERIA TODAY AND TONIGHT. A SOUTHERLY FLOW IS EXPECTED TO CONTINUE AS A DISSIPATING COLD FRONT ARRIVES TODAY. SOME GUSTS TO 20 KNOTS ARE ANTICIPATED AT TIMES HOWEVER, WITH POTENTIALLY HIGHER GUSTS IN AND NEAR ANY STRONGER THUNDERSTORM. OUTLOOK... TUESDAY THROUGH WEDNESDAY NIGHT...SUB SMALL CRAFT ADVISORY CONDITIONS OUTLOOKED WITH THE SURFACE HIGH PRESSURE SYSTEM NEARBY. THURSDAY AND THURSDAY NIGHT...THE CLOSEST PASS TO SMALL CRAFT ADVISORY CONDITIONS AS THE SOUTHWEST GRADIENT INCREASES PRECEDING THE COLD FRONTAL PASSAGE. FOR NOW WE HAVE CONDITIONS PEAKED BELOW CRITERIA. THERE COULD BE SOME SPECIAL MARINE WARNING RELATED PRODUCTS NEEDED. FRIDAY...MORE CONFIDENT ABOUT SUB SMALL CRAFT ADVISORY CONDITIONS BEHIND THE COLD FRONT.
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&& .RIP CURRENTS... A LONG PERIOD /10-12 SECOND/ EAST-SOUTHEAST SWELL LOOKS TO CONTINUE, RESULTING IN A MODERATE RISK OF DANGEROUS RIP CURRENTS THROUGH TONIGHT FOR THE NEW JERSEY AND DELAWARE COASTS. && .PHI WATCHES/WARNINGS/ADVISORIES... PA...NONE. NJ...NONE. DE...NONE. MD...NONE. MARINE...NONE. && $$ SYNOPSIS...GAINES/GIGI NEAR TERM...GORSE SHORT TERM...GORSE LONG TERM...GIGI AVIATION...GIGI/GORSE MARINE...GIGI/GORSE RIP CURRENTS...GORSE

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